Dual-Surface Functionalization of Metal-Organic Frameworks for Enhancing the Catalytic Activity of Candida antarctica Lipase B in Polar Organic Media

One of the most attractive characteristics of metal organic frameworks (MOFs) is their diversity in use as functional materials, because their diversity means that the appropriate MOFs for the required applications can be readily generated from numerous elemental compounds. In addition, post-synthetic modifications of MOFs further expand their diversity. We describe a combined approach involving a typical post-synthetic modification and our previously reported surface modification to introduce multicompounds on MOFs. This method has been used to alter the local environments of a target biocatalyst and has enhanced the activity of the biocatalyst in polar organic media. It has been known that lipases are more active in nonpolar organic solvents than in polar ones. Hence, it can be hypothesized that surrounding lipase molecules with nonpolar compounds possibly increases the activity of lipases in polar organic solvents such as acetonitrile. A series of fatty acids (C12-C22) were conjugated with the amino groups of 2-amino-1,4-benzene dicarboxylate (NH2-BDC) in UiO-66-NH2 (ZrMOF) and then Candida antarctica lipase B (CAL-B) was covalently bonded to the pendent carboxylate groups on the surface of ZrMOF. The introduction of fatty acids around the covalently conjugated CAL-B molecules on ZrMOF improved the activity in acetonitrile by a factor of up to 13.